Auto Air Conditioning & Heater Repair: 2001 2500 Silverado air conditioner, pressure relief valve, orifice tube

Question
When I run the air for 10 to 15 minutes, I hear what sounds like a pressure relief valve opening up (sounds like a tire being punctured). It only lasts about a second but repeats every minute or so until I turn off the air conditioning.
My wife tells me it does the same thing if she turns on the heater too. What could be happening? My wife is scared to use it now. It never did this before.

Answer
Aloha Gary, Tell Mrs.G not to worry it is a common noise from the a/c evaporator when the freon charge is alittle low. The a/c should be checked asap. The cause is when freon is passing thru a very small opening called an orifice tube. It`s  like a pressure regulator.
I`ve had customer tell me it should like a gerggling water noise and air hissing sound. Recommend to check the a/c system at least once a year as maintenance.

Good luck & Aloha, Davidt